Epinephrine mentioned Number stations
Which are quite creepy. So I had a look on YouTube and found this. Watch it from about 1:15.

www.youtube.com/watch?v=EdnoAJ7KoFE

Sleep well.
( sandettie light vessel automatic New Twitter - @bollocksreally, Thu 7 Apr 2011, 23:16, 13 replies)

The video is rather nicely done.
I know in Blighty it's illegal to listen to those.
( Colonel Boris "...a desperate Buzzfeed imitation...", Thu 7 Apr 2011, 23:40, closed)

Which is odd
seeing that the MOD deny they exist.
( sandettie light vessel automatic New Twitter - @bollocksreally, Thu 7 Apr 2011, 23:50, closed)

This was apparently one of the more bizarre stations.
www.simonmason.karoo.net/page12.html
( The Mock TurtIe ™ --- Thinks you are a cunt, on, Thu 7 Apr 2011, 23:43, closed)

Simon Mason
Once gave me a Raleigh racing bike. I had one as a teenager and it goes like poo off a pole.
( sandettie light vessel automatic New Twitter - @bollocksreally, Fri 8 Apr 2011, 0:03, closed)

I'm mystified
I had never heard of number stations until this QOTW.
And I'm not clicking on that link out of fear ;)
What are they. what is their purpose etc?
(insomniac-surfer oh go on then, just this once, Fri 8 Apr 2011, 0:02, closed)

No one is really sure
the general concensus is that they are used to send secret messages to agents in the field. They take the string of numbers and decode them, but how much infor can you convey in repeating the same 5 numbers over and over?

Oh go on, click the link. It's not horses, I promise.
( sandettie light vessel automatic New Twitter - @bollocksreally, Fri 8 Apr 2011, 0:06, closed)

I kept expecting the picture to change to something horrible
and then jump through my screen and rape my soul
( kappynitty doubled your entendre on, Fri 8 Apr 2011, 0:50, closed)

LOL
Ive been wary of clicking links to get that bloody "I love horses" thing
But seriously thtas a very odd thing
(insomniac-surfer oh go on then, just this once, Fri 8 Apr 2011, 1:44, closed)

If memory serves, the Czech Republic has been the only country to date that's openly confirmed its use of number stations in espionage, though that was only after their stations had been decomissioned.
And without the code, the message is completely meaningless - which is probably why the senders are not bothered about sending unencrypted transmissions that can be picked up by anyone in range. For all we know, the number of repetitions might be part of the code itself.

As a method of relaying information, number stations have a lot going for them. They can easily be broadcast from anonymous locations like industrial estates, they use analogue technology so they can't be electronically traced (unlike anything on the internet), and, notwithstanding the efforts of radio enthusiasts, they're hard to detect if you're not looking for them.
( The Mock TurtIe ™ --- Thinks you are a cunt, on, Fri 8 Apr 2011, 2:39, closed)

More importantly
They need nothing more complex than a shortwave radio to receive. Whilst it's probably fairly unusual to see a shortwave radio in somebody's luggage these days, prior to t'internets it was perfectly non-incriminating.
( multijoy, Sat 9 Apr 2011, 12:05, closed)

Have a Wikipedia for them
But as has been said, the idea that they're being used to send agents messages seems to have a lot of legs - using a one time pad, it's possible to send fairly lengthy messages using them. I'm not sure how actively they're used now as there's more interesting and easier ways to do things like that (steganography, for instance).
(A Nony Mouse, Fri 8 Apr 2011, 12:30, closed)

Have none of you played COD Black Op's yet?
It's all based around number stations
( Snollock Biffer I don't really sniff Bollocks, Fri 8 Apr 2011, 19:03, closed)

that one linked is real fucking creepy
im in a nice bright room with the GF, and its really put the willies up...
( RossThePiper Stretch Armstrong is my Father, Thu 14 Apr 2011, 0:00, closed)